Generation of Venus fluorochrome expressing transgenic handmade cloned buffalo embryos using Sleeping Beauty transposon

Abstract

The objective of this study was to optimise the electroporation conditions for efficient integration of Venus construct in buffalo fetal fibroblasts using Sleeping Beauty (SB) based transposition and to produce Venus expressing transgenic cloned embryos through handmade cloning (HMC) approach. Primary culture of buffalo fetal fibroblast cells was established and subsequently cultured cells were co-transfected with Venus and helper plasmid at different combinations of electroporation condition. In different combinations of voltage, time and plasmid dose, we observed that 300 V, single pulse for 10 ms in 2 mm cuvette and 1.5-2.0 μg transposons with 200-300 ng transposase dose was optimum for expressing Venus fluorescence in cells via electroporation. After electroporation, the cells were cultured for 2-3 days and then Venus expressing cells were picked with the help of a Pasteur pipette under the fluorescence microscope to enrich them through single cell culture method before using as donor cells for HMC. In vitro matured oocytes were reconstructed with either transfected or non-transfected buffalo somatic cells by electric fusion followed by activation. The reconstructed, activated embryos were cultured in 400 μL of Research Vitro Cleave medium supplemented with 1% fatty acid-free BSA in 4-well dish, covered with mineral oil and incubated in an incubator (5% CO₂ in air) at 38.5 °C for 8 days and the developmental competence was observed. The percentage of cleaved, 4-8 and 8-16 cells stage embryos generated through Venus expressing cells were comparable with control, whereas, the morula (21.0 vs 53.0%) and blastocysts (10.5 vs 30.6%) produced through Venus expressing cells was found low as compared to control. These results indicate that fetal fibroblasts transfected with Venus could be used as donor cells for buffalo cloning and that Venus gene can be safely used as a marker of foreign gene in buffalo transgenesis.

Keywords: Buffalo; Developmental competence; SCNT; Transgenesis; Transposon.